In modern society, the risk for developing mental health problems have increased year after year and mental health maintenance and promotion is an extremely important challenge to be attacked. The objective evaluation of mood states, which is a factor essential to mental health maintenance and promotion, is considered to be effective in detecting a mental disorder at its early stage and measuring the process of recovery from the disorder. The mood states have been measured subjectively based on the results of interviews and questionnaires in many cases while recently, more objective methods for measuring mood states using biometry have been suggested.
Giving an example, a method has been proposed for measuring the mental states of individuals, such as mood and emotion, using a biospectrometric technology, which is capable of measuring a change (hereinafter, referred to as a Hb signal) in relative concentrations among “oxygenated hemoglobin (Hb)”, “deoxygenated Hb”, and “total Hb (the sum of oxygenated Hb and deoxygenated Hb)” in cerebral cortex by means of any of lights in the visual-to-near-infrared range with high biopermeability (Japanese Unexamined Patent Application Publication No. 2009-285000). Japanese Unexamined Patent Application Publication No. 2009-285000 discloses a method for measuring frontal lobe activation associated with a working memory task using a biospectrometric technology and calculating “mood indices” indicating the mood states of subjects from the obtained values for frontal lobe activation. Working memory (hereinafter, abbreviated to WM in some cases) is the concept of a system, which temporarily stores and manipulates information necessary for various cognitive activities, such as conversation, sentence comprehension, mental calculations, judgment, and inference, and have been advocated as a model for understanding human cognitive function (Baddeley, A., “Working Memory”, Science 255, 556-559 (1992)). The working memory task is a cognitive task, which requires working memory (WM). Initially advocated as a cognitive processing model, WM has been recognized as prefrontal cortex function based on the findings of animal tests and clinical data of human patients with brain injury since the late 1980. Recently, moreover, the development of brain function imaging technology has encouraged the investigations of the neural mechanism of prefrontal cortex function. Giving an example, the studies using functional magnetic resonance imaging (fMRI) demonstrated that when a spatial WM task is performed, dorsolateral prefrontal cortex (DLPFC) of a subject works centering on middle frontal gyrus (Braver, T. S., Cohen, J. D., Nystrom, L. E., Jonides, J., Smith, E. E., Noll, D. C., “A parametric study of prefrontal cortex involvement in human working memory”, NeuroImage 5, 49-62 (1997)).
The method disclosed in Japanese Unexamined Patent Application Publication No. 2009-285000 is characterized in that such a phenomenon is used that frontal lobe activation induced by a verbal WM task using a phonological loop is negatively correlated with the seriousness of depressed mood of a subject, while a frontal lobe activation signal induced by a non-verbal WM task without the need for the phonological loop tends to be not correlated or positively correlated with the seriousness of depressed mood. This biospectrometric technology is expected to be applied to mood measurement in the daily environment because of its negligible restriction on subjects and easiness to measure.
On the other hand, not only mood states but also various differences among individuals, such as the sexuality, age, and WM capacity, of a subject may affect frontal lobe activation associated with a WM task. Giving an example, Nagel I E, Preuschhof C, Li S C, Nyberg L, Baeckman L, Lindenberger U, Heekeren H R. Performance level modulates adult age differences in brain activation during spatial working memory. Proc Natl Acad Sci USA. 2009; 106(52):22552-7 describes that a brain activation signal associated with a WM task is modified by both of the factors: subject's age and task performance.